cl1 = 0.5;
Point(1) = {0, 0, 0, cl1};
Point(2) = {1, 0, 0, cl1};
Point(3) = {1, 1, 0, cl1};
Point(4) = {0, 1, 0, cl1};
Line(1) = {1, 4};
Line(2) = {4, 3};
Line(3) = {3, 2};
Line(4) = {2, 1};
Line Loop(6) = {2, 3, 4, 1};
Plane Surface(6) = {6};
PEC = 999;
Physical Line(PEC) = {1,2,3,4};
cl1 = 0;
Physical Surface(cl1) = {6};
